1. Field of the Invention
The present invention relates to a connecting mechanism, an optical signal cable, and an optical communication cable production method for fixing an optical fiber which transmits an optical signal and a plug for connecting the tip of the optical fiber to another apparatus.
2. Description of the Related Art
Conventionally, when connecting a plurality of electronic apparatuses, dedicated signal cables are used, and connectors are used for the connection between the signal cables and the electronic apparatuses. For example, normally, by inserting a plug or jack that is fitted to the end of the signal cable into a jack or plug provided in the electronic apparatus, it is possible to establish a connection between the signal cable and the electronic apparatus.
Recently, for the signal cables which are being used for connecting individual electronic apparatus, not only are conventionally known electrical signal cables used, but also, for example, optical signal cables which use light to perform information transmission are used.
Silica glass, compound glass, or plastic is used to produce the optical fibers used in the optical signal cables. In particular, special connectors are generally used when plastic optical fibers are connected together, or to connect light emitting parts, light receiving parts, etc. of components and apparatuses.
As shown in FIG. 8, a connector which forms a connection mechanism of an optical cable 10 which is capable of transmitting optical signals is constructed of a plug 2 and a jack 12. The plug 2 is fitted to an end of the optical cable 10, whereas the jack 12 is installed in, for example, the back of an electronic apparatus. With such a connector, by fitting the plug 2 into the jack 12, optical signals are transmitted and received inside the jack 12 between the tip of the core of the optical cable 10 which reaches the vicinity of the end of the plug 2 and a light emitting/receiving part (not shown in this figure) in the electronic apparatus 11.
When optically connecting light emitting/receiving elements etc. with the optical fiber, the plug 2 used as a connector has a hollow section and the optical fiber is inserted into this hollow section and the tip of the optical fiber is fixed. Thus the plug 2 forms a highly reliable connection. A metal such as aluminum, stainless steel, brass, or engineering plastic is used as the material. In particular, since the end face is pressed against a heating plate to fix the optical fiber, a heat resistant material is preferable.
Conventionally, for fixing the plug and the tip of the optical fiber, the optical fiber cover part is clamped by the connector, a ferrule part at the end of the connector and the optical fiber are bonded by filling an adhesive therebetween, or teeth-like hooks are formed inside the plug and the inserted optical fiber is caught thereby; and then, after fixing, processing is performed on the tip of the optical fiber which protrudes from the end of the plug.
FIG. 1 is a partial sectional view showing the connection state between an optical fiber, in particular, the optical signal cable 10 which is formed of an optical fiber, and a light receiving part of an electronic apparatus. An optical fiber 1 has a portion of a cover 6 cut off at the tip to expose the core and is inserted into a penetrating hole of the plug 2. The end part of the optical fiber cover 6 abuts against a step portion formed at the boundary between a small diameter section and a large diameter section of the penetrating hole of the plug 2, and a clamping part 7 is formed at a certain portion of the cover 6, thus fixing the plug 2 and the optical fiber 1.
Light emitted by an LED or a laser and transmitted along the inside of the optical fiber 1 emerges from the tip of the optical fiber 1, is focussed by a lens 13a of a light receiving device 13 in the electronic apparatus, and is received as an optical signal at a light receiving part 13b. It is not always necessary to provide the lens 13 in the light receiving device 13.
In fixing the tip of the core of the optical fiber 1 and the ferrule part of the plug 2, as described above, the clamping part 7 is formed at the portion where the cover 6 of the optical fiber and the plug 2 overlap, or they are bonded. However, when the cable 10 is bent and straightened, in a phenomenon referred to as pistoning, wherein the core of the optical fiber is pushed out and pulled in from the ferrule part at the end of the plug 2, the core moves in and out over a 1-mm region, as indicated by d in FIG. 1. This may cause the light receiving part 13 of the electronic apparatus to break or may cause the level of transmitted light to be greatly reduced. Moreover, when adhesive is used, the optical characteristics may be adversely influenced in some cases.
As shown in FIGS. 2A and 2B, as a measure to prevent pistoning, the tip of the core of the optical fiber 1 is formed into the shape of a mushroom, thus forming a convex part. The optical fiber 1 has a portion of the cover cut off at the tip to expose the core and is inserted into the penetrating hole of the plug 2. The length of the portion of the optical fiber 1 from which the cover has been removed is arranged to be just barely larger than the length of the small diameter section of the penetrating hole in the plug 2 shown in FIG. 1. Accordingly, when the end of the cover of the optical fiber abuts against the step portion formed at the boundary between the small diameter section and the large diameter section of the penetrating hole in the plug 2, the tip of the optical fiber 1 partially protrudes.
Here, if the core which is pushed out from the end of the plug 2 is pressed against a concave surface section of a heating apparatus 5 used for molding, the surface of the heated optical fiber 1 melts, a convex part is formed at the tip of the optical fiber 1 by the concave surface section of the heating apparatus 5, the mushroom shape covers the end of the plug, and the fiber 1 becomes fixed. If molding is performed in this fashion, since a portion of the hat of the mushroom-shape at the tip and the end of the plug 2 are in contact, the core cannot easily retract. However, it is difficult to prevent it from being pushed out, and furthermore, since the end portion of the mushroom shape at the tip of the optical fiber 1, from which the optical signal transmitted along the inside of the optical fiber 1 is emitted, is exposed, it can easily be damaged.
Furthermore, by molding the tip of the optical fiber into the mushroom shape thus forming a dome shape, when the shape of the tip is a curved surface, it is difficult for the emerging light to return. As a result, the accuracy of bi-directional communication is also improved.
Accordingly, in conventional methods for fixing the tip of an optical fiber core and plug, since the optical characteristics are degraded by directly clamping the core of the optical fiber, the plug 2 clamps the cover 6 which protects the optical fiber from above, and the fixing is indirectly performed by, for example, forming the clamping part 7 or pressing a clip. However, due to optical limitations, since it is not possible to securely fix the optical fiber and the cable cover portion, in fixing the cover of the cable with the plug from above, the core of the optical fiber is caused to move slightly in the axial direction by bending and pulling of the cable and the connection positional accuracy of the connector is thus reduced.
In order to prevent this, there are methods for directly bonding the plug and the optical fiber by an adhesive. However, this results in increased production costs and, furthermore, there is a significant adverse influence on the optical characteristics. Accordingly, in fixing optical fibers and plugs by conventional means, the in-and-out movement of the core cannot be completely prevented, and there is a problem in that the cable is not ideally suited for use in recent electronic devices which transmit and receive signals at high speed.
It is an object of the present invention to provide a connecting mechanism for transmitting an optical signal between another apparatus and an optical fiber while retaining the optical fiber which transmits the optical signal. The connecting mechanism includes an insertion part through which the optical fiber is inserted. The insertion part has a tapered portion at at least one internal diameter section close to an end thereof. The connecting mechanism also includes a fixing groove, provided in the tapered portion of the insertion part, which fixes the optical fiber to the connecting mechanism by causing an expanded part, which is created as a result of melting a tip of the optical fiber that is inserted in the insertion part, to flow into the fixing groove and solidify.
Another object of the present invention is to provide an optical signal cable which transmits an optical signal and which emits and/or receives the optical signal to/from another apparatus. The optical signal cable includes an optical fiber which transmits the optical signal, and a connecting part which attachably and removably connects to the other apparatus while retaining the optical fiber. The connecting part has an insertion part for inserting the optical fiber through the inner diameter thereof; a tapered portion which is formed to taper outwardly at the inner circumference of at least one end of the insertion part; and at least one fixing groove formed in part of the tapered portion and into which an expanded part, which is created by melting a tip of the optical fiber, flows and solidifies.
Another object of the present invention is to provide an optical communication cable production method, wherein a thermomolding apparatus is used to fix an optical fiber to a connecting mechanism which retains the optical fiber, the connecting mechanism being provided with a fixing part for fixing the optical fiber to part of a tapered portion which is formed by outwardly tapering the inside part of one end of a penetrating hole which is provided inside the connecting mechanism to allow the optical fiber, which transmits an optical signal, to be inserted therethrough. The method comprises a step of inserting the optical fiber into the penetrating hole in the connecting mechanism; a step of heating a tip of the inserted optical fiber with the thermomolding apparatus; and a step of stopping the heating by the thermomolding apparatus when an expanded part, which is created by melting the tip of the optical fiber as a result of heating the tip of the optical fiber with the thermomolding apparatus, has flowed into the fixing part.